EMPLOYEE WAS WALKING AROUND THE PLANT INSPECTING EQUIPMENT AND MAKING ADJUSTMENT TO F-20 FAN FOR PRODUCTION PURPOSES WHEN HE SOMEHOW STEPPED IN SOME GREASE. DURING THE ABOVE PROCESS HE THEN WE NT DOWN A FLIGHT OF STAIRS TO RETURN TO THE CONTROL ROOM WHEN HE SLIPPED ON THE STEP AND FELL APPROXIMATELY 6 STAIRS BEFORE CATCHING HIMSELF AND COMING TO A STOP.